MSD 6a vs. HEI - Team Camaro Tech
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post #1 of 9 (permalink) Old Apr 28th, 09, 11:08 AM Thread Starter
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Marc
 
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MSD 6a vs. HEI

What is (is there?) the biggest advantage to going to the MSD ingition? I currently have an Accel coil on a stock HEI distributor. What will the upgraded ignition do for me?
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post #2 of 9 (permalink) Old Apr 28th, 09, 02:07 PM
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Re: MSD 6a vs. HEI

I've only started reading about different types of ignition systems; so I hope someone will correct me if I'm wrong. There are two basic types of set-ups available: inductive ignition and CD (capacitive discharge) ignition. HEI operates on the inductive system which requires that the coil ramp battery/alternator power to create the spark. As you can imagine, higher RPMs will give the coil less time to di it's job in this situation. The CD ignition uses capacitors to provide an initial step-up in power before hitting the coil. This step-up happens very quickly, allowing multiple sparks at lower RPMs. As is the case with inductive ignitions, higher RPMs give the capacitors less time to charge; however unlike inductive ignitions, it isn't very detrimental to the performance of the system. Instead, the system drops is the multiple-spark advantage, yielding to a single spark around 3000 RPM. It is my understanding that MSD pioneered and remains the leader in CD ignition systems.

What does all that mean? If you're looking for ultimate performance at high RPMs, go with a CD ignition system. It will also help ignite the mixture in forced-induction engines (super- or turbocharged). If you have a more pedestrian engine, the HEI system will work well for the application and probably be the better alternative. In a CD system, a separate ignition box is needed in addition to the distributor and coil. Conversely, in an inductive ignition system, you only need the distributor and coil. Having more components only mean there are more things that can go wrong. If you've been following my saga of ignition problems, you'll realize that I've had to replace the distributor, the coil and now the ignition box. It's not cheap. Furthermore, there are high performance HEI modules available that will offer increased performance and hooter spark to a 7000 maximum RPM. Needless to say, since my cars are more street-performance oriented, my next build will be using an HEI system.

Here is a link to a magazine article for your topic: http://www.chevyhiperformance.com/te...ics/index.html
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post #3 of 9 (permalink) Old Apr 28th, 09, 05:32 PM Thread Starter
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Marc
 
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Re: MSD 6a vs. HEI

octanefueled- Thank you! Excellent information and made my decision to stay with my HEI (and save some $$) a no-brainer.
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post #4 of 9 (permalink) Old Apr 28th, 09, 05:44 PM
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Re: MSD 6a vs. HEI

The biggest single improvement you can make to an old car is an electronic ignition. It sucked keeping a set of plugs clean with points. An HEI is the most reliable distributor made. If it fits in your car you're done. The MSD is more hardcore but on a street motor you won't notice a difference. Save your money for other things.
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post #5 of 9 (permalink) Old Apr 28th, 09, 07:24 PM
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Re: MSD 6a vs. HEI

Reliability and the availability of HEI parts was the decision maker for me (I have a street mobile). HEI preforms well enough. MSD boxes haven't impressed me much. The fact that the multispark feature poops out at moderate RPM kind of defeats the purpose IMHO. Search the archives for people with MSD problems and that'll be another reason to consider HEI. <flame suit on>

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68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI
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post #6 of 9 (permalink) Old Apr 29th, 09, 10:20 AM
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Re: MSD 6a vs. HEI

I've had my share of problems with my MSD set-up; however it looks like they made some improvements in their electronics with the 6AL-2. I'm runnig the CD ignition because I've got a little too much compression for the street. Like I said, my next build will run HEI and a more tame compression.



Quote:
Originally Posted by dnult View Post
Reliability and the availability of HEI parts was the decision maker for me (I have a street mobile). HEI preforms well enough. MSD boxes haven't impressed me much. The fact that the multispark feature poops out at moderate RPM kind of defeats the purpose IMHO. Search the archives for people with MSD problems and that'll be another reason to consider HEI. <flame suit on>
Multiple sparks at lower RPM should also help with fuel economy and throttle response by ensuring more complete combustion. Then again, if you rally need a CD ignition, you might not be too concerned about fuel economy. I'm getting single-digit mpg...
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post #7 of 9 (permalink) Old Apr 29th, 09, 10:52 AM
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Re: MSD 6a vs. HEI

I tried a MSD 6AL on my EFI setup...made no difference in idle quality, driveability or ET, so I took it off.

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post #8 of 9 (permalink) Old Apr 29th, 09, 10:57 AM Thread Starter
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Marc
 
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Re: MSD 6a vs. HEI

Thanks one and all. I saved some money and got the better choice of ignition too.
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post #9 of 9 (permalink) Old May 1st, 09, 07:55 PM
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Dave
 
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Re: MSD 6a vs. HEI

Well when i had points and added an msd 6al box it starrted quicker and idled better. The last couple years since i've had a pro billet distributor its been eating a cap a year, not to mention the 5 year old 6al box that died. If an hei would fit in my z28 i'd give up a litlle high rpm performance just to have the reliability and ease of not having to mail order parts. Honestly every year the car gets closer to factory gm parts just for reliabilty. I'm not trying to knock msd but hei parts can be had anywhere.
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